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Diffusion and He Overabundances: Hydrodynamical Implications

Published online by Cambridge University Press:  12 April 2016

G. Michaud
G. Michaud*
Affiliation:
Département de PhysiqueUniversité de MontréalC.P. 6128, Succ. A, MontréalCANADAH3C 3J7

Abstract

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In the absence of mass loss, diffusion leads to underabundances of He in main sequence stars. Because of a very strong observational link with Ap and He weak stars, it has however been suggested that diffusion is the explanation for the He rich stars of the upper main sequence. This requires a mass loss rate of 10−12 Mo yr−1 or slightly lower. The mass loss rate must decrease as Teff increases. Magnetic fields must apparently be involved to reduce the mass loss rate. Since this model predicts that the CNO abundances should be normal in the cooler He rich stars, it leads to a clear observational test. Detailed calculations should be made to confirm the importance of this test. The effects of separation in the wind, the atmosphere and the envelope are discussed to conclude that separation in the atmosphere is likely to be most important. The importance of diffusion for He rich white dwarfs and horizontal branch stars are briefly discussed.

Type
IX Theory
Information
International Astronomical Union Colloquium , Volume 87: Hydrogen Deficient Stars and Related Objects , 1985 , pp. 453 - 469
Copyright
Copyright © Reidel 1986

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